This invention relates to xerography. More particularly, this invention relates to corona generating devices for applying electrostatic charge onto a photoreceptor.
In the xerographic process, a photoreceptor comprising a photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed in a pattern to be reproduced. This exposure discharges the receptor areas in accordance with the radiation intensity which reaches them and thereby creates an electrostatic latent image on or in the receptor coating which may then be developed into visible form by applying a developer material, e.g., a liquid or a powder, to the receptor using any development technique generally known and used in the art. The developer material electrostatically clings to the receptor in a visual pattern corresponding to the electrostatic image. Thereafter, the developed image is transferred from the receptor to a support material such as paper to which it may be fixed, thereby forming a permanent print.
The charging of the photoreceptor in preparation for the exposure step can be accomplished by a corona-generating device. The corona-generating device applies electrostatic charge to the photoreceptor to raise it to a potential of, e.g., approximately 500 to 1000 volts. One form of corona generating device for this purpose is disclosed in U.S. Pat. No. 2,777,957 wherein a plurality of parallel wires are connected in series to a high voltage source and are supported in a conductive shield that is arranged in closely spaced relation to the surface to be charged. When the wires are energized, corona is generated along the surface of the wires and ions are caused to be deposited on the adjacent photoconductive surface. A mechanism is usually provided to effect relative movement of the surface to be charged and the corona-generating device. Some corona generating devices may have a single corona wire instead of a plurality of wires. Designs that are more recent include a “grid” or screen spaced in between the coronode and the receptor to control the amount of ions that reach the receptor.
As described in U.S. patent application Ser. No. 12/062,169, entitled “High Strength, Light Weight Corona Wires Using Carbon Nanotube Yarns” to Zona et al., the entire disclosure of which is incorporated herein by reference, nanostructured Carbon Nano Tube (CNT) filament can be used as a linear coronode to improve upon the life and performance of the wire in conventional corotrons. A coronode is a corona-generating electrode. A corotron is a corona-generating device that is used to apply charge to a photoreceptor. From testing commercially available CNT filaments as coronode members, it was learned that these filaments facilitate corona charging similar to that of tungsten wires, and because they are lightweight and mechanically stronger than tungsten, they enable much smaller diameters than have been possible using tungsten wires.
It is also desirable in corona generating devices to provide an arrangement for easily replacing a deteriorated corona electrode with a new one. Since this replacement usually takes place at a commercial site by a service technician, ease of replacement and adjustment in a minimum amount of time is very beneficial.
However, xerographic charging devices typically suffer from short operational lives and high run costs. Others have tried to solve these problems. For example, U.S. Pat. No. 6,308,032 entitled “Rotatable Charging Apparatus, and Printing Machine Including the Same” to Weber et al., discloses a plural solid state charging devices positioned around a cylinder. An individual charging device is used for its lifetime. Then, the device rotates to expose another charging device. This use of a charging device, and then rotating to another position, is a way of indexing to achieve consistent charging uniformity for a long use period.
Existing devices, even with minor improvements, are projected to fall short of meeting life and cost objectives for future systems. At present, a variety of performance restorative cleaning mechanisms and devices have been implemented to attempt to improve life coronode-based chargers. Unfortunately, these attempted improvements have had only limited success while adding cost and complexity to the subsystem. To address the shortfall, radically different charger devices, such as a solid-state charger, have been the focus of research over the past decade where attempts were made to leverage emerging technologies to address life and cost issues.